This invention relates to a device for indicating the state of EM or AM security tags and to a method of determining the state of activation of EM or AM security tags.
Security tags of this type are being increasingly used in department stores and warehouses for the electronic surveillance of articles. They are comprised of a strip of a soft magnetic material as, for example, Permalloy or a magnetic glass, which is characterized by high permeability and low coercive force. Arranged parallel thereto and in close vicinity to the strip of soft magnetic material is a strip of a semi-hard or hard magnetic material having a relatively high coercive force as, for example, SEMIVAVC from the Vacuumschmelze company.
In acousto-magnetic (AM) security tags the strip of semi-hard or hard magnetic material is a one-piece construction, while in electromagnetic (EM) security tags it is divided into several sections spatially separated from each other.
In a surveillance zone which preferably is arranged in the entrance or exit area of the department store or warehouse to be protected, an alternating magnetic field is emitted. This alternating field excites the soft magnetic material of the activated security tag into emitting a characteristic signal. This signal is detected by a detecting device sensitive in the frequency range of the signal and evaluated as an identification signal for an article leaving the surveillance zone in unauthorized manner; an alarm is released.
The detecting device should cease to respond to the security tag once the merchandise has been rightly purchased. Therefore, the security tag is deactivated after proper purchase of the article. In cases where EM security tags are involved, this is accomplished by driving the semi-hard or hard magnetic strip into saturation, its magnetization hence suppressing a response of the soft magnetic material to the alternating magnetic field in the surveillance zone. With AM security tags, deactivation is accomplished, for example, by demagnetizing the semi-hard or hard magnetic strip.
Typically, security tags are affixed in deactivated state to the goods or their packaging already at the point of manufacture. These goods are subsequently packaged or transferred to pallets for distribution. To simplify merchandise logistics, it should not be necessary in future to remove the articles from their packaging or pallets for activation, but rather, activation should take place in a one-step operation for all the safety tags contained in a packaging or on a pallet.
For the operator of a department store in which the articles are to be sold it is of eminent importance to have reliable knowledge of the statexe2x80x94activated or deactivatedxe2x80x94 of the security tags. If articles with deactivated security tags reach the sales floor, the entire electronic article surveillance system is useless. However, the state of the security tags cannot be read from the tags directly.
It is an object of the present invention to provide a device which indicates simply and reliably the state of one or several security tags.
According to the present invention, this object is accomplished by a device for indicating the state of EM security tags or AM security tags, comprising a first semi-hard or hard magnetic layer and a second layer arranged in close vicinity thereto, wherein said second layer is sensitive to magnetic fields.
This device has the advantage that, when affixed to a packaging or a pallet, its first layer adopts the same state of magnetization as the semi-hard or hard magnetic layer of the security tags contained in the packaging or on the pallet. In consequence, from the magnetization state of the first layer of the device a conclusion can be drawn as to the activated or deactivated state of the security tags in the packaging or on the pallet. The second, magnetically sensitive layer of the device enables the magnetization state of the first layer to be inspected visually, thereby obviating the need to provide measuring devices for measuring the magnetization state.
In one embodiment of the invention the second layer is comprised of a ferrofluid, so that with the first layer in a magnetized state the magnetic particles suspended in the fluid concentrate in the zone of high magnetic field strength. This effects a color change of the zones. Where the magnetic field is weak, the number of magnetic particles decreases, producing overall a distinct contrast between the zones with a strong magnetic field and the zones where the magnetic field is weak. This contrast enables the state of the security tags to be determined.
When the device of the invention is utilized to indicate the state of EM security tags, the presence of a contrast in the second layer is indicative of deactivated EM security tags. In the case of acousto-magnetic (AM) security tags the presence of a contrast in the second layer indicates that the AM security tags are activated.
In one variant of the invention provision is made for enclosing the second layer between two plates and a circumferential frame to prevent the ferrofluid from escaping and to make sure that the device of the invention operates reliably regardless of the position.
As a provision supplementary to the invention, at least one of the plates, in particular the plate arranged on the side of the second layer opposite the first layer, is transparent to enable the viewer of the device to see at a glance whether or not there is a contrast.
In a further embodiment of the invention, the second layer is comprised of a magneto-optically active material so that the optical properties, in particular the refractive index, of the second layer changes when the first layer is magnetized. By illuminating the second layer with polarized light, for example, the changes in the optical properties due to the existing magnetic field can be made visible, which enables the state of the security tags to be clearly established also when these materials are employed.
In one embodiment of the invention the second layer is comprised of a film material which affords flexibility and economy of manufacture of the device of the invention.
Further embodiments provide for the first layer to be composed of several sections and for the first layer or the sections to be in the form of letters or figures. This enables a plain text to become visible in the second layer when the security tags or the device of the invention is magnetized. This plain text may read, for example, xe2x80x9cdeactivatedxe2x80x9d to indicate the state of EM security tags, or xe2x80x9cactivatedxe2x80x9d to indicate the state of AM security tags.
As another provision supplementary to the invention, a carrier layer is arranged between the first layer and the second layer to increase the mechanical strength of the device of the invention.
One embodiment of the invention provides for the first layer and the second layer to be in essentially parallel arrangement to each other so that the optical changes of the second layer resulting from the degree of magnetization of the first layer are equal over the entire dimension of the second layer.
In an advantageous embodiment of the invention the device includes elements for fastening to a packaging or a pallet so that it can be fastened simply and securely to these shipping containers. These elements can be of the type including an eyelet, a hook, an adhesive or the like.
The object initially referred to is also solved by a method of determining the state of activation of EM or AM security tags which includes the steps of
attaching a device for indicating the state of EM or AM security tags to a packaging or a pallet containing merchandise equipped with EM or AM security tags,
simultaneously activating or deactivating all the security tags in the packaging or on the pallet and the device for indicating the state of EM or AM security tags in a device for activating or deactivating security tags, and
establishing the state of activation of the EM or AM security tags in the packaging or on the pallet by reading the device for indicating the state of EM or AM security tags.
This method has the advantage of enabling the state of all security tags present in close spatial proximity to the device to be detected by reading a device for indicating the state of EM or AM security tags. This results in an increased safety of the electronic article surveillance system. Activating the security tags and the indicating device simultaneously requires activators/deactivators whose magnetic fields are sufficiently strong to activate or deactivate all security tags and the indicating device at the same time.